Abstract:

The goal of this project was to develop and test non-herbicidal techniques that remove nonnative
plant or weed seeds from the top 2 inches of the soil. The Nature Conservancy (TNC) is
currently restoring prairies in the Willamette Valley. Some areas of the Pacific Northwest have
already seen loss of more than 99% of former native prairie and 90% oak savanna to agriculture,
forest production, and development. In order for the land to be restored, all non-native vegetation
must be removed, beginning with removal of unwanted vegetation and a reduction of weed seed
density in the soil (Greg Fitzpatrick, 2006). Non-native or invasive plant species pose a serious
threat to revegetation with native species, and the cost of weed management is prohibitive if
herbicides are not used.
We tested two strategies to remove weed seeds from the soil. In the first project we
worked collaboratively with mechanical engineering (ME) students to develop a machine that
would kill seeds in the soil with heat. We tested weed seed survival after exposure to various
temperatures and provided the data to the ME students that so that they could adequately design
and build the machine. We also evaluated the efficacy of their machine after it was built. In the
second project we measured the potential seed loss due to carabid beetle weed seed predation in
a controlled environment. The non-native species of choice for these studies represented a broad
range of environmental adaptability and included Pigweed (Aamaranthus retroflexus), Oxeye
Daisy (Chysanthemum leucanthemum), Wild Carrot (Daucus carota), and False Brome
(Brachypodium sylvaticum), Proso Millet (Panicum miliaceum), Hairy Nightshade (Solanaceae)
or (Solanum sarrachoides) (see appendix I for more information on the characteristics of these
species).